Tof camera, motor vehicle, method for producing a tof camera and method for determining a distance to an object

ABSTRACT

A TOF camera for determining a distance to an object comprising: a radiation source configured to emit electromagnetic radiation toward the object, radiation-sensitive sensor elements configured and arranged to detect the electromagnetic radiation reflected/scattered by the object, an optical element arranged to influence the emitted electromagnetic radiation in the radiation path of the reflected/scattered electromagnetic radiation between the object and the sensor elements, a computing unit electrically connected to the radiation source and sensor elements configured to determine a time duration required by the electromagnetic radiation from the radiation source to the object; from the object to the sensor elements; and to determine the distance between the TOF camera and the object depending on the time duration determined. The sensor elements and/or the optical element are configured such that different sensor elements detect the reflected/scattered electromagnetic radiation from different solid angles on the far side of the optical element.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Patent Application Serial No.DE 10 2017 204 073.4, which was filed Mar. 13, 2017, and is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The invention relates to a TOF camera, a motor vehicle, a method forproducing a TOF camera, and a method for determining a distance to anobject.

SUMMARY

A conventional TOF (Time Of Flight) camera, which is also referred to asa PMD (Photonic Mixing Device) camera, comprises a TOF sensor, whichgenerally is also referred to as a PMD sensor and hereinafter simply as“sensor arrangement”. Such a sensor arrangement comprises a plurality ofsensor elements, which are often arranged in matrix form, that is to sayin rows and columns, and which are each light-sensitive. A TOF camera isa 3D camera system that measures distances from the TOF camera to anobject by the time of flight (TOF, also ToF) method. To that end, aregion, also called scene, in the field of view of the camera isirradiated by means of a radiation pulse and the TOF camera measures,for each pixel, that is to say for each sensor element, the time neededby the corresponding electromagnetic radiation to reach the object andreturn again. The required time is directly proportional to thedistance. The TOF camera thus yields for each pixel the distance of theobject imaged thereon. The principle corresponds to laser scanning withthe advantage that an entire region is recorded all at once and need notbe scanned. A TOF camera is used nowadays for example in a motor vehiclefor measuring a distance between the motor vehicle and some othertraffic object or in a robot for recognizing an obstacle.

The electromagnetic radiation used can be for example light in thevisible range, infrared radiation or UV radiation. The sensorarrangement can comprise a filter, or a filter can be optically disposedupstream of the sensor arrangement, which filter transmits onlyelectromagnetic radiation in the wavelength range of the emittedelectromagnetic radiation. A good signal-to-noise ratio can be achievedas a result.

The electromagnetic radiation emitted by a radiation source of theconventional TOF camera has a symmetrical radiation distribution, inparticular a Gaussian or a Lambertian radiation distribution. In thecase of these radiation distributions, a radiation intensity is thehighest along the axis of symmetry of the radiation and falls withincreasing distance from the axis of symmetry. In general, the axis ofsymmetry of the radiation is perpendicular to an optically activesurface of the radiation source by which the electromagnetic radiationis emitted. In a manner corresponding thereto, in the case of theconventional TOF camera, the sensor elements each detect electromagneticradiation from a specific solid angle, wherein the solid angles haveidentical magnitudes.

In order to obtain a good signal-to-noise ratio, it is advantageous toalign the TOF camera such that the object to which the distance is to bemeasured lies on the axis of symmetry of the radiation and thus in theregion of the highest radiation intensity. Alternatively oradditionally, the TOF camera can be aligned such that the object isarranged centrally in the detected solid angles. In other words, the TOFcamera, if a good signal-to-noise ratio is to be achieved, has to bealigned such that the object is arranged frontally in front of the TOFcamera and/or centrally in a field of view of the TOF camera. Thefurther away the object is from the axis of symmetry, the worse thesignal-to-noise ratio becomes. Therefore, the TOF camera has to bealigned depending on the region in which the object is situated relativeto the TOF camera. Aligning the TOF camera can be carried outlaboriously by hand or by means of a complex actuator arrangement.Furthermore, aligning the TOF camera is not always possible, in whichcase a poor signal-to-noise ratio must then be accepted. A poorsignal-to-noise ratio can lead to an inaccurate determination of thedistance from the TOF camera to the object.

One problem addressed is that of providing a TOF camera which enables ina simple manner a particularly precise determination of a distance to anobject whose relative position in relation to the TOF camera is known.

One problem addressed is that of providing a motor vehicle in which aprecise determination of a distance to an object whose relative positionin relation to the motor vehicle is known is possible in a simplemanner.

One problem addressed is that of providing a method for producing a TOFcamera which can be carried out simply, rapidly and/or cost-effectivelyand/or which contributes to a precise determination of a distance to anobject whose relative position in relation to the TOF camera is knownbeing possible by means of the TOF camera in a simple manner.

One problem addressed is that of providing a method for operating a TOFcamera which can be carried out simply, rapidly and/or cost-effectivelyand/or which contributes to a precise determination of a distance to anobject whose relative position in relation to the TOF camera is knownbeing possible by means of the TOF camera in a simple manner.

One problem addressed is solved by means of a TOF camera for determininga distance to an object, comprising a radiation source, which isconfigured to emit electromagnetic radiation in a direction toward theobject, a plurality of radiation-sensitive sensor elements, which areconfigured and arranged such that they detect the electromagneticradiation reflected and/or scattered by the object, an optical element,which is arranged for the purpose of influencing the reflected and/orscattered electromagnetic radiation in the radiation path of thereflected and/or scattered electromagnetic radiation between the objectand the sensor elements, and a computing unit, which is electricallyconnected to the radiation source and the sensor elements and which isconfigured to determine a time duration required by the electromagneticradiation from the radiation source to the object and from the object tothe sensor elements and to determine the distance between the TOF cameraand the object depending on the time duration determined, wherein thesensor elements and/or the optical element are/is configured such thatdifferent sensor elements from among the latter detect the reflectedand/or scattered electromagnetic radiation from correspondinglydifferent solid angles on the far side of the optical element and thatat least some of the far-side solid angles have different magnitudes.

If consideration is given to one of the sensor elements and thecorresponding solid angle observed by means of said sensor element, thenthe signal-to-noise ratio is all the better, the smaller thecorresponding solid angle. The better the signal-to-noise ratio, themore precisely it is possible to determine the distance to an article,for example the object or a part of the object, which is arranged withinthe solid angle. This applies to each of the sensor elements and thecorresponding solid angles. If a relative position of the object withrespect to the TOF camera is known or can be anticipated, then thefar-side solid angles can be set such that the object is arranged atparticularly small solid angles from among the far-side solid anglesduring the distance measurement. Detecting the reflected and/orscattered electromagnetic radiation from the far-side solid angleshaving different magnitudes therefore makes it possible, in a simplemanner, that the distance to the object can be determined particularlyprecisely, in particular on account of a very good signal-to-noiseratio. This holds true even if the object is not arranged frontally infront of the TOF camera, is not arranged centrally in a field of view ofthe TOF camera and/or is not arranged along a straight line that isperpendicular to an optically active surface of a sensor arrangementwhich comprises the sensor elements.

The far-side solid angles are solid angles which extend from a side ofthe optical element facing away from the sensor elements into ahalf-space situated on the side of the optical element facing away fromthe sensor elements. In other words, the far-side solid angles are solidangles which lie on the far side of the optical element as viewed fromthe sensor elements. In contrast thereto, near-side solid angles aresolid angles which extend from the sensor elements to the opticalelement and which are situated between the optical element and thesensor elements. In other words, the near-side solid angles are solidangles which are situated on the near side of the optical element asviewed from the sensor elements.

The sensor elements can form a TOF sensor and/or a PMD sensor. Theradiation source can comprise one, two or more electromagneticradiation-emitting components, for example LEDs and/or OLEDs. Theelectromagnetic radiation can comprise or be light in the visible range,IR radiation and/or UV radiation.

Optionally an optical filter can be arranged between the object and thesensor elements, which filter transmits to the sensor elements onlyelectromagnetic radiation having wavelengths corresponding to thewavelengths of the electromagnetic radiation emitted by the radiationsource. This can contribute to the fact that the signal-to-noise ratiois particularly good and the fact that the distance can be determinedparticularly precisely.

In accordance with one development, the optical element and/or thesensor elements are configured such that the magnitudes of the far-sidesolid angles are adapted to a region in which the object is expectedproceeding from the TOF camera. In particular, the solid angle or solidangles in which the region lies is or are particularly small comparedwith the solid angles in which the region does not lie. If it is known,for example, for what purpose the TOF camera is intended to be used, inparticular in what situations distances to what objects are intended tobe identified, and where the region is arranged relative to the TOFcamera, then the magnitudes of the far-side solid angles can be adaptedsuch that the solid angle or solid angles in which said region lies isor are particularly small. If the object then appears in the regionduring intended use of the TOF camera, the signal-to-noise ratio isparticularly good during the determination of the distance to theobject, for which reason the distance to the object can then bedetermined particularly precisely. To put it clearly, the magnitudes ofthe solid angles are coordinated exactly with the use and arrangement ofthe TOF camera during the operation of the TOF camera, as a result ofwhich the distance to an object in a region in which the object istypically expected in the case of said use and said arrangement of theTOF camera can be determined particularly precisely.

In accordance with one development, the optical element and/or thesensor elements are/is configured such that one or a plurality of thefar-side solid angles within which the region lies is or are smallerthan the far-side solid angles within which the region does not lie. Inother words, the magnitudes of the solid angles are adapted in such away that the region lies in a partial segment of the field of view ofthe TOF camera in which the solid angles assigned to the individualsensor elements are particularly small relative to other partialsegments of the field of view of the TOF camera. This contributes to thefact that the signal-to-noise ratio is particularly good during thedetermination of the distance to the object in the region, and thus thefact that the distance to the object in the region can be determinedparticularly precisely.

In accordance with one development, the optical element and/or thesensor elements are configured such that, in the case of a dynamicvariation of the region, the magnitudes of the far-side solid angles areadapted depending on the dynamic variation of the region. By way ofexample, a position of the region relative to the TOF camera can bedynamically varied if the region moves relative to the TOF camera, forexample if the region and/or the TOF camera move(s). In other words, theobject may be expected in one region at a first point in time and theobject may be expected in another region after a certain time durationhas elapsed, for example because the object and/or the TOF cameramove(s). In this context, a movement of the region relative to the TOFcamera is tantamount to the object being expected in one region at onepoint in time and being expected in another region at another point intime. If the region moves relative to the TOF camera or the object isexpected in one region at one point in time and is expected in the otherregion at another point in time, then the magnitudes of the solid anglescan be dynamically adapted to this movement and/or for change,specifically such that a particularly good signal-to-noise ratio canstill be achieved. This can be achieved, for example, by the magnitudesof the solid angles being adapted such that the partial segment of thefield of view of the TOF camera which lies within the smallest solidangles observed by the corresponding sensor elements follows the movingregion or is aligned with the region at the new position.

In accordance with one development, the sensor elements are configuredsuch that different sensor elements from among the latter detect theelectromagnetic radiation that has passed through the optical elementfrom correspondingly different solid angles on the near side of theoptical element and that at least some of the near-side solid angleshave different magnitudes. By way of example, the near-side solidangles, that is to say the solid angles which lie between the sensorelements and the optical element and which are respectively assigned toone of the sensor elements, may already have different magnitudes. Thatis to say that, by means of different sensor elements from among thelatter, areas of the optical element having correspondingly differentsizes are observed. These different magnitudes of the near-side solidangles are then transferred to the different magnitudes of thecorresponding far-side solid angles by means of the optical element. Inthis case, the optical element may or may not influence the differencein the magnitudes of the solid angles. In other words, the opticalelement may be a partial source of the differences in the magnitudes ofthe solid angles or merely transfer the differences in the magnitudes ofthe near-side solid angles. In still other words, the differentmagnitudes of the far-side solid angles may result exclusively from thedifferent magnitudes of the near-side solid angles. As an alternativethereto, the different magnitudes of the far-side solid angles mayresult from the different magnitudes of the near-side solid angles andthe influence of the optical element. The sensor arrangement maycomprise, for the purpose of providing the different magnitudes of thenear-side solid angles, different sensor elements, for example, by meansof which solid angles having different magnitudes can be observed.

As an alternative thereto, the different magnitudes of the far-sidesolid angles may result exclusively from the properties of the opticalelement. That is to say that the near-side solid angles may all have thesame magnitude, for which purpose, for example, exclusively structurallyidentical sensor elements can be used. The optical element then ensuresthat electromagnetic radiation is directed from different solid angleshaving different magnitudes onto corresponding sensor elements fromamong the latter.

In accordance with one development, the sensor elements may beconfigured such that the magnitudes of the near-side solid angles areadapted depending on the dynamic variation of the region. Adapting themagnitudes of the near-side solid angles depending on the dynamicvariation of the region can contribute to dynamically adapting themagnitudes of the far-side solid angles to the dynamic variation of theregion, since, on account of the optical element, a variation of themagnitudes of the near-side solid angles varies the magnitudes of thefar-side solid angles. In other words, it is possible to react to thedynamic variation of the region with a dynamic variation of themagnitudes of the near-side solid angles, as a result of which themagnitudes of the far-side solid angles can be adapted to the dynamicvariation of the region. The magnitudes of the near-side solid anglescan be adapted for example by virtue of the sensor elements beingconfigured such that the sizes of their fields of view are adaptable,for example by means of adjustable diaphragms.

In accordance with one development, the sensor elements form a camera.In other words, the sensor arrangement is a camera.

In accordance with one development, the optical element may comprise atleast one asymmetrical optical surface arranged such that the reflectedand/or scattered electromagnetic radiation passes through theasymmetrical optical surface. As an alternative or in addition to thesensor elements, therefore, the optical element, in particular theasymmetrical optical surface, is configured such that it contributes tothe different magnitudes of the solid angles. By way of example, thenear-side solid angles can have identical magnitudes and, on account ofthe optical element and the asymmetrical optical surface thereof,far-side solid angles having different magnitudes can be observed bymeans of the sensor elements which all observe areas of the opticalelement having the same size and all have a field of view having thesame size. This may contribute to the fact that detecting theelectromagnetic radiation from the solid angles having differentmagnitudes is possible in a particularly simple and/or cost-effectivemanner. As an alternative thereto, the sensor elements can contribute bymeans of observing near-side solid angles having different magnitudes orareas of the optical element having different sizes and the opticalelement can also contribute by means of additionally varying themagnitude ratios of the different solid angles with respect to oneanother.

The asymmetrical optical surface may be an entrance surface of theoptical element, for example, through which the reflected and/orscattered electromagnetic radiation proceeding from the object entersthe optical element. As an alternative thereto, the asymmetrical opticalsurface may be an exit surface of the optical element, for example,through which the electromagnetic radiation leaves the optical elementin a direction toward the sensor elements. As an alternative thereto,the asymmetrical optical surface may be a surface within the opticalelement, for example. Furthermore, the optical element may have two ormore of the optical surfaces mentioned above, which are arranged onebehind another in the beam path of the electromagnetic radiation andwhich cooperate in order to generate the first asymmetrical radiationdistribution.

If the optical surface forms the entrance surface or the exit surface ofthe optical element, then this can be produced for example by shaping ofthe optical element and/or by means of surface treatment of the opticalelement, for example by means of grinding or by means of a laser. If theoptical surface lies in the optical element and is at a distance fromthe entrance surface and the exit surface, then the optical surface canbe produced for example by means of internal engraving, for example bymeans of a laser.

In accordance with one development, the optical element is configuredsuch that the asymmetrical optical surface is adapted depending on thedynamic variation of the region. Adapting the optical surface dependingon the dynamic variation of the region can contribute to dynamicallyadapting the magnitudes of the solid angles to the dynamic variation ofthe region. In other words, it is possible to react to the dynamicvariation of the region with a dynamic variation of the optical surface,as a result of which the magnitudes of the solid angles can be adaptedto the dynamic variation of the region. The optical surface can bedynamically adapted for example by virtue of the optical element beingconfigured such that the beam paths of the emitted electromagneticradiation are variable and in particular adaptable, as a result of whichthe local radiation intensity is adaptable. By way of example, theoptical element can comprise one, two or more electrically drivablefluid lenses, the entrance surfaces and/or exit surfaces of which can bevaried with the aid of electrical voltages.

In accordance with one development, the asymmetrical optical surface isconfigured as radiation-diffracting, radiation-refracting and/orsegmented. This can contribute, in a particularly simple manner, toobserving solid angles having different magnitudes by means of thesensor elements.

In accordance with one development, the optical surface is configured ina made to measure manner depending on the region. In other words, theoptical element and/or the optical surface are/is tailored (referred toas: tailored lens). To put it clearly, firstly what is determined is howthe region is configured during intended use of the TOF camera and wherethe region is arranged relative to the TOF camera, in other words wherethe object is expected proceeding from the TOF camera, and then theoptical surface is configured with dimensional accuracy, in particularwith register accuracy with respect to the region. In particular, theoptical surface is configured such that the region is illuminated orirradiated particularly well during intended use of the TOF camera.

In accordance with one development, the TOF camera comprises a housing,in which the radiation source, the sensor elements, the computing unitand the optical element are arranged.

One problem addressed by the invention is solved by means of a motorvehicle comprising the TOF camera, wherein the object is a trafficobject. The traffic object can be for example another road user, forexample another motor vehicle, a cyclist or a pedestrian, or any articlesituated in the vicinity of the motor vehicle, for example a trafficsign, a guardrail or traffic lights. If the TOF camera is arranged forexample at a front or at a rear side of the motor vehicle, then onaccount of the solid angles having different magnitudes an objectsituated laterally in front of or laterally behind the motor vehicle cannevertheless be detected very well, in particular with a very goodsignal-to-noise ratio, and the distance to said object can be determinedparticularly precisely. If the TOF camera is arranged for example on aside of the motor vehicle, then on account of the solid angles havingdifferent magnitudes an object situated laterally in front of orlaterally behind the motor vehicle can nevertheless be detected verywell, in particular with a very good signal-to-noise ratio, and thedistance to said object can be determined particularly precisely. If themotor vehicle moves relative to the object, then the solid angles havingdifferent magnitudes can be dynamically adapted in such a way that thesolid angles that encompass the region in which the object is currentlysituated are particularly small, as a result of which a particularlyprecise determination of the distance to the object is possible at everypoint in time.

The developments and/or advantages explained above in association withthe TOF camera can readily be applied to the motor vehicle.

One problem addressed by the invention is solved by means of a methodfor producing a TOF camera for determining a distance to an object,wherein a radiation source is arranged for emitting electromagneticradiation in a direction toward the object, a plurality ofradiation-sensitive sensor elements are arranged such that they detectthe electromagnetic radiation reflected and/or scattered by the object,a computing unit is configured to determine a time duration required bythe electromagnetic radiation from the radiation source to the objectand from the object to the receiver and to determine the distancebetween the TOF camera and the object depending on the time durationdetermined, and is electrically connected to the radiation source andthe sensor elements, and an optical element is arranged for the purposeof influencing the reflected and/or scattered electromagnetic radiationin the radiation path of the reflected and/or scattered electromagneticradiation between the object and the sensor elements, wherein the sensorelements and/or the optical element are/is configured and arranged suchthat different sensor elements from among the latter detect thereflected and/or scattered electromagnetic radiation fromcorrespondingly different solid angles on the far side of the opticalelement and that at least some of the far-side solid angles havedifferent magnitudes.

The developments and/or advantages explained above in association withthe TOF camera and the motor vehicle can readily be applied to themethod for producing the TOF camera.

One problem addressed by the invention is solved by means of a methodfor determining a distance to an object, wherein electromagneticradiation is emitted in a direction toward the object by means of aradiation source, the electromagnetic radiation is detected fromdifferent solid angles by means of a plurality of sensor elements,wherein at least part of the detected electromagnetic radiation isreflected and/or scattered by the object and wherein at least some ofthe solid angles have different magnitudes, a time duration isdetermined which is required by the electromagnetic radiation from theradiation source to the object and from the object to the receiver, andthe distance to the object is determined depending on the time durationdetermined. The developments and/or advantages explained above inassociation with the TOF camera and the motor vehicle can readily beapplied to the method for determining the distance to the object.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments of the invention are described with reference to thefollowing drawings, in which:

FIG. 1 shows a schematic illustration of a conventional TOF camera andof an object;

FIG. 2 shows a conventional optical element and a conventional sensorarrangement;

FIG. 3 shows a conventional optical element and a conventional sensorarrangement;

FIG. 4 shows a schematic illustration of the conventional TOF camera andof the object in accordance with FIG. 1;

FIG. 5 shows a schematic illustration of one exemplary embodiment of aTOF camera and of an object;

FIG. 6 shows one exemplary embodiment of an optical element and of asensor arrangement;

FIG. 7 shows a schematic side view of one exemplary embodiment of anoptical element and of a sensor arrangement;

FIG. 8 shows one exemplary embodiment of an optical element;

FIG. 9 shows one exemplary embodiment of an optical element;

FIG. 10 shows one exemplary embodiment of a motor vehicle.

DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form part of this description and show forillustration purposes specific exemplary embodiments in which theinvention can be implemented. Since components of exemplary embodimentscan be positioned in a number of different orientations, the directionterminology serves for illustration and is not restrictive in any waywhatsoever. It goes without saying that other exemplary embodiments canbe used and structural or logical changes can be made, without departingfrom the scope of protection of the present invention. It goes withoutsaying that the features of the various exemplary embodiments describedherein can be combined with one another, unless specifically indicatedotherwise. The following detailed description should therefore not beinterpreted in a restrictive sense, and the scope of protection of thepresent invention is defined by the appended claims. In the figures,identical or similar elements are provided with identical referencesigns, insofar as this is expedient.

FIG. 1 shows a schematic illustration of a conventional TOF camera 2 andof an object 32. The conventional TOF camera 2 serves for determining adistance D between the conventional TOF camera 2 and the object 32. Theobject 32 is arranged in a first region 42.

The conventional TOF camera 2 comprises a conventional radiation source4 for emitting electromagnetic radiation 14, a conventional emitter-sidelens 6 for focusing or collimating the emitted electromagnetic radiation14, a conventional optical element 7, a radiation-sensitive conventionalsensor arrangement 8 and a conventional computing unit 10, which arearranged in a conventional housing 12.

During operation of the conventional TOF camera 2, the conventionalradiation source 4 emits the electromagnetic radiation 14, which isinfluenced, for example focused or collimated, by means of theconventional emitter-side lens 6. The conventional TOF camera 2 isaligned such that the emitted electromagnetic radiation 14 impinges onthe object 32. The object 32 reflects and/or scatters at least part ofthe electromagnetic radiation 14, such that reflected and/or scatteredelectromagnetic radiation 16 passes through the conventional opticalelement 7, impinges on the conventional sensor arrangement 8 and isdetected by the latter.

The conventional computing unit 10 determines a time duration requiredby the electromagnetic radiation 14, 16 to pass from the conventionalradiation source 4 as far as the conventional sensor arrangement 8. Theconventional computing unit 10 determines the distance D depending onthe time duration determined and the speed of light.

FIG. 2 shows the conventional optical element 7 and the conventionalsensor arrangement 8. The principle underlying the conventional opticalelement 7 and the conventional sensor arrangement 8 is the same as in amulti-aperture camera and which in English is also referred to as“optical stitching of segments”. The conventional optical element 7comprises a plurality of conventional lenses L1, L2, L3, L4, L5. Thesensor arrangement 8 comprises a plurality of conventional sensorelements S1, S2, S3, S4, S5, which are arranged on a conventionalcarrier 18. The conventional lenses L1, L2, L3, L4, L5 are respectivelyassigned to one of the sensor elements S1, S2, S3, S4, S5. Theconventional lenses L1, L2, L3, L4, L5 focus the reflected and/orscattered electromagnetic radiation 16 coming from the object 32 ontothe corresponding sensor elements S1, S2, S3, S4, S5, wherein theelectromagnetic radiation 16 originates in each case from a specificconventional solid angle 17. These conventional solid angles 17 aresituated on the far side of the conventional optical element 7 as viewedfrom the conventional sensor arrangement 8 and are therefore referred toas conventional far-side solid angles 17. Consequently, exactly one ofthe conventional far-side solid angles 17 can be assigned to each paircomprising one of the conventional lenses L1, L2, L3, L4, L5 and thesensor element S1, S2, S3, S4, S5 assigned to said conventional lens L1,L2, L3, L4, L5.

The electromagnetic radiation 16 that has passed through theconventional lenses L1, L2, L3, L4, L5 is focused onto the correspondingsensor elements S1, S2, S3, S4, S5. Each of the conventional lenses L1,L2, L3, L4, L5 is arranged at a corresponding conventional solid angle19 on the near side of the optical element 7 as viewed from thecorresponding sensor element S1, S2, S3, S4, S5. Therefore, theseconventional solid angles 19 are also referred to as conventionalnear-side solid angles 19.

The conventional far-side solid angles 17 have identical magnitudes.Moreover, the conventional near-side solid angles 19 have identicalmagnitudes.

A signal-to-noise ratio of a signal representative of the distance D isall the better, the smaller the conventional solid angles 17, 19. To putit clearly, the signal-to-noise ratio of the signal is all the better,the smaller the region observed by means of one of the sensor elementsS1, S2, S3, S4, S5.

FIG. 3 shows an alternative conventional optical element 7 and theconventional sensor arrangement 8. The principle underlying theconventional optical element 7 and the conventional sensor arrangement 8is the same as in a single-aperture camera. The conventional opticalelement 7 comprises two conventional lenses L5, L6, which are arrangedone behind the other in the beam path of the reflected and/or scatteredelectromagnetic radiation 16. The sensor arrangement 8 comprises theplurality of conventional sensor elements S1, S2, S3, S4, S5. Bothconventional lenses L6, L7 are assigned to all the sensor elements S1,S2, S3, S4, S5. The conventional lenses L6, L7 direct the reflectedand/or scattered electromagnetic radiation 16 coming from the object 32onto the sensor elements S1, S2, S3, S4, S5. Each of the sensor elementsS1, S2, S3, S4, S5 detects the reflected and/or scatteredelectromagnetic radiation 16 from a respective specific conventionalsolid angle 17. These conventional solid angles 17 are situated on thefar side of the conventional optical element 7 as viewed from theconventional sensor arrangement 8 and are therefore referred to asconventional far-side solid angles 17. Consequently, exactly one of theconventional far-side solid angles 17 can be assigned to each sensorelement S1, S2, S3, S4, S5. The conventional far-side solid angles 17have identical magnitudes.

A signal-to-noise ratio of a signal representative of the distance D isall the better, the smaller the conventional solid angles 17. To put itclearly, the signal-to-noise ratio of the signal is all the better, thesmaller the region observed by means of one of the sensor elements S1,S2, S3, S4, S5.

FIG. 4 shows a schematic illustration of the conventional TOF camera 2in accordance with FIG. 1 and of the conventional object 32, wherein theobject 32 is arranged in a second region 44, which is situated alongsidethe first region 42. Moreover, FIG. 4 depicts a third region 46, whichis arranged on a side of the second region 44 facing away from the firstregion 42.

In FIG. 4, in order to simplify the illustration, the first, second andthird regions 42, 44, 46 are depicted as different regions arrangedalongside one another. In reality, the first, second and third regions42, 44, 46 can actually be regarded as different regions. As analternative thereto, however, the first, second and third regions 42,44, 46 may merely represent different positions of one moving region. Byway of example, the predefined region can correspond to the first region42 at a first point in time, can correspond to the second region 44 at asecond point in time and can correspond to the third region 46 at athird point in time. In other words, the first, second and third regions42, 44, 46 can be representative of a movement of the predefined region.

Independently of where the object 32 is situated, in particular whetherit is situated in the first region 42, in the second region 44 or in thethird region 46, the distance D to the object 32 is always detected withthe same precision on account of the conventional far-side solid angles17 having identical magnitudes and the uniform signal-to-noise ratioresulting therefrom. If it is then known, however, that the object 32preferably stays in one of the regions 42, 44, 46 or that the object 32moves with high probability from one of the regions 42, 44, 46 toanother of the regions 42, 44, 46, the conventional TOF camera 2 affordsno possibility of being able to ascertain the distance D with increasedprecision on the basis of these known boundary conditions.

FIG. 5 shows a schematic illustration of one exemplary embodiment of aTOF camera 20 and of an object 32. The TOF camera 20 serves fordetermining the distance D between the TOF camera 20 and the object 32.The object 32 is arranged in the second region 44 in the situationillustrated.

The TOF camera 20 comprises a radiation source 24, a lens element 26, anoptical element 27, a radiation-sensitive sensor arrangement 28 and acomputing unit 30, which are arranged in a housing 22. The radiationsource 24 can comprise one, two or more light emitting components, forexample LEDs, OLEDs and/or laser diodes. Optionally, the radiationsource 24 can comprise one, two or more radiation-influencing elements,such as, for example, lenses and/or filters and/or radiation-refracting,radiation-scattering or radiation-diffracting elements. The lens element27 can comprise for example one, two or more lenses and/or opticalsurfaces. The optical element 27 can comprise for example one, two ormore lenses and/or optical surfaces. The sensor arrangement 28 cancomprise two or more sensor elements T1, T2, T3, T4, T5 (see FIG. 6),for example photosensors. The computing unit 30 can comprise one, two ormore microchips, electronic circuits, processors and/or storage units.

During operation of the TOF camera 20, the radiation source 24 emitselectromagnetic radiation 34, which is influenced, for example focusedand/or collimated, by means of the lens element 27. The TOF camera 20can be driven by means of the computing unit 30, for example. The TOFcamera 20 can modulate for example the electromagnetic radiation 34, forexample in the form of a sinusoidal signal or a rectangular signal. TheTOF camera 20 is aligned such that the emitted electromagnetic radiation24 impinges on the object 32. The object 32 reflects and/or scatters atleast part of the electromagnetic radiation 24, such that reflectedand/or scattered electromagnetic radiation 36 passes through the opticalelement 27, impinges on the sensor arrangement 28 and is detected by thelatter.

The computing unit 30 determines a time duration required by theelectromagnetic radiation 34, 36 to pass from the radiation source 24 asfar as the sensor elements T1, T2, T3, T4, T5. To that end, thecomputing unit 30 can determine for example a phase shift between theemitted electromagnetic radiation 34 and the received electromagneticradiation 36. The computing unit 30 determines the distance D dependingon the time duration determined and the speed of light.

FIG. 6 shows one exemplary embodiment of the optical element 7 and ofthe sensor arrangement 28. The principle underlying the optical element27 and the sensor arrangement 28 is similar to that of themulti-aperture camera explained with reference to FIG. 2. The opticalelement 27 comprises a plurality of lenses M1, M2, M3, M4, M5. Thesensor arrangement 28 comprises a plurality of sensor elements T1, T2,T3, T4, T5, which are arranged on a carrier 28. The lenses M1, M2, M3,M4, M5 are respectively assigned to one of the sensor elements T1, T2,T3, T4, T5. In particular, a first lens M1 is assigned to a first sensorelement T1, a second lens M2 is assigned to a second sensor element T2,a third lens M3 is assigned to a third sensor element T3, a fourth lensM4 is assigned to a fourth sensor element T4, and a fifth lens M5 isassigned to a fifth sensor element T5. The lenses M1, M2, M3, M4, M5focus the reflected and/or scattered electromagnetic radiation 36 comingfrom the object 32 onto the corresponding sensor elements T1, T2, T3,T4, T5, wherein the electromagnetic radiation 36 respectively originatesfrom a specific solid angle PHI1, PHI2, PHI3, PHI4, PHI5. These solidangles PHI1, PHI2, PHI3, PHI4, PHI5 are situated on the far side of theoptical element 27 as viewed from the sensor arrangement 28 and aretherefore referred to as far-side solid angles PHI1, PHI2, PHI3, PHI4,PHI5. Consequently, exactly one of the far-side solid angles PHI1, PHI2,PHI3, PHI4, PHI5 is assigned to each pair comprising one of the lensesM1, M2, M3, M4, M5 and the sensor element T1, T2, T3, T4, T5 assigned tosaid lens M1, M2, M3, M4, M5.

In particular, a first far-side solid angle PHI1 can be assigned to thefirst sensor element T1 and the first lens M1. A second far-side solidangle PHI2 can be assigned to the second sensor element T2 and thesecond lens M2. A third far-side solid angle PHI3 can be assigned to thethird sensor element T3 and the third lens M3. A fourth far-side solidangle PHI4 can be assigned to the fourth sensor element T4 and thefourth lens M4. A fifth far-side solid angle PHI5 can be assigned to thefifth sensor element T5 and the fifth lens M5.

Consequently, the electromagnetic radiation 36 coming from the firstsolid angle PHI1 passes through the first lens M1 and is detected by thefirst sensor element T1. The electromagnetic radiation 36 coming fromthe second solid angle PHI2 passes through the second lens M2 and isdetected by the second sensor element T2. The electromagnetic radiation36 coming from the third solid angle PHI3 passes through the third lensM3 and is detected by the third sensor element T3. The electromagneticradiation 36 coming from the fourth solid angle PHI4 passes through thefourth lens M4 and is detected by the fourth sensor element T4. Theelectromagnetic radiation 36 coming from the fifth solid angle PHI5passes through the fifth lens M5 and is detected by the fifth sensorelement T5.

The electromagnetic radiation 36 that has passed through the lenses M1,M2, M3, M4, M5 is focused onto the corresponding sensor elements T1, T2,T3, T4, T5. Each of the lenses M1, M2, M3, M4, M5 is arranged at acorresponding solid angle 29 on the near side of the optical element 27as viewed from the sensor element T1, T2, T3, T4, T5. Therefore, thesesolid angles 29 are also referred to as near-side solid angles 29.

The far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5 have differentmagnitudes. In particular, the third far-side solid angle PHI3 isgreater than the second and fourth far-side solid angles PHI2, PHI4, andthe second and third far-side solid angles PHI2, PHI3 are greater thanthe first and fifth far-side solid angles PHI1, PHI5. A signal-to-noiseratio of a signal representative of the distance D is all the better,the smaller the solid angles PHI1, PHI2, PHI3, PHI4, PHI5. To put itclearly, the signal-to-noise ratio of the signal is all the better, thesmaller the region observed by means of one of the sensor elements T1,T2, T3, T4, T5. Consequently, the distance D to the object 32 in thecase of the exemplary embodiment shown in FIG. 6 can be determined themost precisely if the object 32 lies within the third far-side solidangle PHI3. For the exemplary embodiment shown in FIG. 6, this would bethe case if the object 32 were arranged centrally in front of theoptical element 27 and/or the sensor arrangement 28, in particular inthe first region 42.

If it is known, however, that, in the case of a specific application forwhich the TOF camera 20 is to be used, the object 32 is regularlyarranged in a different region 42, 44, 46 or expected there, then anoptical element 27 adapted to said application can be used therefor. Inthe case of said optical element 27 it is then possible to ensure thatthe far-side solid angle PHI1, PHI2, PHI3, PHI4, PHI5 at which theobject 32 is normally arranged or normally expected in the case of thisapplication is particularly small. In this way, the optical element 27can be optimized even for applications in which the object 32 normallyis not arranged or expected centrally in front of the TOF camera 20.

FIG. 7 shows a schematic side view of an exemplary embodiment of anoptical element 27 and of a sensor arrangement 28, which may largelycorrespond to the optical element 27 and sensor arrangement 28respectively explained with reference to FIG. 6. In contrast to theexemplary embodiment shown in FIG. 6, however, the exemplary embodimentshown in FIG. 7 is optimized toward the object 32 not being situatedcentrally in front of the TOF camera 20, but rather to the left thereofrelative to the figures, for example in the second region 44 or in thethird region 46. Since it is assumed that the object 32 is situated inthe second region 44 or at least that the object 32 is expected in thesecond region 44, the far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5are set such that the second region 44 lies at particularly smallfar-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5 from among thelatter. In particular, the first and second far-side solid angles PHI1,PHI2 are relatively small and the third far-side solid angle PHI3 isrelatively large in comparison with the exemplary embodiment explainedwith reference to FIG. 6. As a result, a very good signal-to-noise ratiocan be achieved by means of the TOF camera 20 even though the object 32is not situated centrally in front of the TOF camera 20, for whichreason the distance D to the object 32 can be determined very precisely.

Optionally, the lenses M1, M2, M3, M4, M5 of the optical element 27illustrated in FIGS. 6 and 7 can each be driven such that the magnitudesof the corresponding far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5are variable. Upon a variation of the optical surfaces of the lenses M1,M2, M3, M4, M5, the far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5assigned to the corresponding lenses M1, M2, M3, M4, M5 change as well.By way of example, in a first drive state of the optical element 27, oneof the far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5 can then havea predefined magnitude and, in a second drive state, the same solidangle PHI1, PHI2, PHI3, PHI4, PHI5 can have a different magnitude thanin the first drive state. To that end, by way of example, the lenses M1,M2, M3, M4, M5 can each have at least one optical surface that isdynamically variable. By way of example, the lenses M1, M2, M3, M4, M5,and in particular the optical surfaces, are variable by means ofelectric current and/or by means of electrical voltage. By way ofexample, the lenses M1, M2, M3, M4, M5 are electrically drivable fluidlenses.

In this case, FIGS. 6 and 7 may show the same exemplary embodiments ofthe optical element 27 and of the sensor arrangement 28, wherein FIG. 6illustrates a drive state which is optimized for example toward theobject 32 being situated frontally in front of the TOF camera 20, inparticular frontally in front of the optical element 27 and the sensorarrangement 28, for example in the first region 42. In contrast thereto,FIG. 7 illustrates a drive state which is optimized toward the object 32in FIG. 5 having moved toward the left and then being situated laterallyin front of the TOF camera 20, in particular laterally in front of theoptical element 27 and the sensor arrangement 28, for example in thesecond region 44 or in the third region 46.

Consequently, if the object 32 moves, the magnitudes of the far-sidesolid angles PHI1, PHI2, PHI3, PHI4, PHI5 can be adapted in such a waythat the region 42, 44, 46 in which the object 32 is then situated onaccount of its movement is covered with the smallest possible far-sidesolid angles PHI1, PHI2, PHI3, PHI4, PHI5. In this case, even in theevent of a movement of the object 32, a very good signal-to-noise ratiocan be achieved by means of the TOF camera 20, for which reason thedistance D to the object 32 can be determined very precisely at anytime.

The near-side solid angles 29 have identical magnitudes in the case ofthe exemplary embodiments shown in FIGS. 6 and 7. However, the near-sidesolid angles 29 can also be adapted to the region 42, 44, 46 in whichthe object 32 is arranged or expected in the case of the correspondingapplication, or to the movement of the object 32, in a mannercorresponding to the far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5.In particular, the near-side solid angles 29 assigned to the sensorelements T1, T2, T3, T4, T5 which are expected to detect the object 32can be particularly small. This can be achieved in particular bycorresponding design of the sensor elements T1, T2, T3, T4, T5.Consequently, the corresponding TOF camera 20 can be adapted to thedesired application by targeted adaptation of the near-side and/orfar-side solid angles 29, PHI1, PHI2, PHI3, PHI4, PHI5.

FIG. 8 shows one exemplary embodiment of an optical element 27, forexample of the optical element 27 explained above. The optical element27 comprises a lens comprising an asymmetrical optical surface 70. Theoptical element 27 having the asymmetrical optical surface 70 can beused as an alternative to the optical elements 27 shown in FIGS. 6 and 7in the case of the TOF camera 20 that was explained with reference toFIG. 5. The asymmetrical optical surface 70 has the effect that thereflected and/or scattered electromagnetic radiation 36 that passesthrough the optical element 27 subsequently has an asymmetricalradiation distribution, and that the far-side solid angles PHI1, PHI2,PHI3, PHI4, PHI5 assigned to the sensor elements T1, T2, T3, T4, T5 havedifferent magnitudes.

FIG. 9 shows one exemplary embodiment of an optical element 27, forexample of the optical element 27 explained above. The optical element27 can be used as an alternative to the optical elements 27 shown inFIGS. 6, 7 and 8 in the case of the TOF camera 20 that was explainedwith reference to FIG. 5. The optical element 27 comprises a firstsegment 72, a second segment 74, a third segment 76 and a fourth segment78. The optical element 27 comprises the asymmetrical optical surface70. The optical surface 70 comprises a first partial surface 82 formedat the first segment 72, a second partial surface 84 formed at thesecond segment 74, a third partial surface 86 formed at the thirdsegment 76, and a fourth partial surface 88 formed at the fourth segment78. The partial surfaces 82, 84, 86, 88 can each be configured in asymmetrical or asymmetrical fashion. If the partial surfaces 82, 84, 86,88 are symmetrical in each case, then they are configured differentlyfrom one another and arranged in such a way that overall the opticalsurface 70 is asymmetrical. The asymmetrical optical surface 70 has theeffect that the reflected and/or scattered electromagnetic radiation 36that passes through the optical element 27 subsequently has anasymmetrical radiation distribution, and that the far-side solid anglesPHI1, PHI2, PHI3, PHI4, PHI5 assigned to the sensor elements T1, T2, T3,T4, T5 have different magnitudes.

In the case of the optical elements 27 explained with reference to FIGS.8 and 9, the asymmetrical optical surfaces 70 are formed in each case atan exit surface of the corresponding optical element 27. As analternative thereto, the asymmetrical optical surfaces 70 can also beformed at the entrance surfaces of the corresponding optical elements 27or at inner surfaces of the corresponding optical elements 27, saidinner surfaces being spaced apart from the entrance surfaces and exitsurfaces.

FIG. 10 shows one exemplary embodiment of a motor vehicle 90 comprisinga TOF camera 20, for example one of the TOF cameras 20 explained abovewith reference to FIGS. 5 to 9. The TOF camera 20 is arranged forexample at a front of the motor vehicle 90. As an alternative thereto,the TOF camera 20 can also be arranged at the rear or at one of thesides of the motor vehicle 90. Furthermore, in addition to the one TOFcamera 20, one, two or more further TOF cameras 20 can be arranged inthe motor vehicle 90. In the motor vehicle 90 the TOF camera 20 servesfor determining the distance D to the object 32, which in this contextis a traffic object, for example a pedestrian, a cyclist, another motorvehicle or a guardrail.

On account of the design of the motor vehicle 90 and on account of thestructure of the TOF camera 20, the latter is arranged such that a frontside of the TOF camera 20 and in particular a front side of theradiation source 24 of the TOF camera 20 are aligned perpendicularly tothe direction of travel. However, the TOF camera 20 is intended to beused to determine distances D to objects 32 which are not arrangeddirectly frontally in front of the motor vehicle 90, but rather arearranged laterally in front of the motor vehicle 90 in a manner offsetwith respect to the direction of travel. Therefore, the TOF camera 20 isconfigured such that it generates the far-side solid angles PHI1, PHI2,PHI3, PHI4, PHI5 having different magnitudes, specifically such that theregion 42, 44, 46 in which the object 32 will most likely appear and/orwhich is intended to be monitored with the highest accuracy is coveredby means of the smallest far-side solid angles PHI1, PHI2, PHI3, PHI4,PHI5. If the TOF camera 20, as explained above, is configured such thatthe magnitudes of the far-side solid angles PHI1, PHI2, PHI3, PHI4, PHI5are variable, then the region 42, 44, 46 in which the distance D can bedetermined with the greatest precision can be correspondingly varied ormoved.

The invention is not restricted to the embodiments indicated. By way ofexample, the embodiments can be combined with one another. By way ofexample, the optical element 27 can be part of the sensor arrangement28. Furthermore, more or fewer regions 42, 44, 46 can be provided.Furthermore, more or fewer sensor elements T1, T2, T3, T4, T5, more orfewer lenses M1, M2, M3, M4, M5, optical elements 27 and/or more orfewer segments 72, 74, 76, 78 can be provided.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

1. A TOF camera for determining a distance to an object, comprising aradiation source, which is configured to emit electromagnetic radiationin a direction toward the object, a plurality of radiation-sensitivesensor elements, which are configured and arranged such that they detectthe electromagnetic radiation reflected and/or scattered by the obj ect,an optical element, which is arranged for the purpose of influencing thereflected and/or scattered electromagnetic radiation in the radiationpath of the reflected and/or scattered electromagnetic radiation betweenthe object and the sensor elements, and a computing unit, which iselectrically connected to the radiation source and the sensor elementsand which is configured to determine a time duration required by theelectromagnetic radiation from the radiation source to the object andfrom the object to the sensor elements and to determine the distancebetween the TOF camera and the object depending on the time durationdetermined, wherein the sensor elements and/or the optical elementare/is configured such that different sensor elements from among thelatter detect the reflected and/or scattered electromagnetic radiationfrom correspondingly different solid angles on the far side of theoptical element and that at least some of the far-side solid angles havedifferent magnitudes.
 2. The TOF camera as claimed in claim 1, whereinthe optical element and/or the sensor elements are configured such thatthe magnitudes of the far-side solid angles are adapted to a region inwhich the object is expected proceeding from the TOF camera.
 3. The TOFcamera as claimed in claim 2, wherein the optical element and/or thesensor elements are/is configured such that one or a plurality of thefar-side solid angles within which the region lies is or are smallerthan the far-side solid angles within which the region does not lie. 4.The TOF camera as claimed in claim 2, wherein the optical element and/orthe sensor elements are configured such that, in the case of a dynamicvariation of the region, the magnitudes of the far-side solid angles areadapted depending on the dynamic variation of the region.
 5. The TOFcamera as claimed in claim 1, wherein the sensor elements are configuredsuch that different sensor elements from among the latter detect theelectromagnetic radiation that has passed through the optical elementfrom correspondingly different near-side solid angles on the near sideof the optical element and that at least some of the near-side solidangles have different magnitudes.
 6. The TOF camera as claimed in claim4, wherein the sensor elements are configured such that the magnitudesof the near-side solid angles are adapted depending on the dynamicvariation of the region.
 7. The TOF camera as claimed in claim 6,wherein the sensor elements form a camera.
 8. The TOF camera as claimedin claim 1, wherein the optical element comprises at least oneasymmetrical optical surface arranged such that the reflected and/orscattered electromagnetic radiation passes through the asymmetricaloptical surface.
 9. The TOF camera as claimed in claim 8, wherein theoptical element is configured such that the asymmetrical optical surfaceis adapted depending on the dynamic variation of the region.
 10. The TOFcamera as claimed in claims 8, wherein the asymmetrical optical surfaceis configured as radiation-diffracting, radiation-refracting and/orsegmented.
 11. The TOF camera as claimed in claim 8, wherein the opticalsurface is configured in a made to measure manner depending on theregion.
 12. The TOF camera as claimed in claim 1, comprising a housing,in which the radiation source, the sensor elements, the computing unitand the optical element are arranged.
 13. The TOF camera as claimed inclaim 1, wherein the TOF camera is arranged in a motor vehicle.
 14. TheTOF camera as claimed claim 1, wherein the object is a traffic object.15. A method for producing a TOF camera for determining a distance to anobject, wherein a radiation source is arranged for emittingelectromagnetic radiation in a direction toward the object, a pluralityof radiation-sensitive sensor elements are arranged such that theydetect electromagnetic radiation reflected and/or scattered by theobject, a computing unit is configured to determine a time durationrequired by the electromagnetic radiation from the radiation source tothe object and from the object to the sensor elements and to determinethe distance between the TOF camera and the object depending on the timeduration determined, and is electrically connected to the radiationsource and the sensor elements, and an optical element is arranged forthe purpose of influencing the reflected and/or scatteredelectromagnetic radiation in the radiation path of the reflected and/orscattered electromagnetic radiation between the object and the sensorelements, wherein the sensor elements and/or the optical element are/isconfigured such that different sensor elements from among the latterdetect the reflected and/or scattered electromagnetic radiation fromcorrespondingly different solid angles on the far side of the opticalelement and that at least some of the far-side solid angles havedifferent magnitudes.
 16. A method for determining a distance to anobject, wherein electromagnetic radiation is emitted in a directiontoward the object by means of a radiation source, reflected and/orscattered electromagnetic radiation is detected from different solidangles by means of a plurality of sensor elements, wherein at least partof the detected reflected and/or scattered electromagnetic radiation isreflected and/or scattered by the object and wherein at least some ofthe solid angles have different magnitudes, a time duration isdetermined which is required by the electromagnetic radiation from theradiation source to the object and from the object to the sensorelements, and the distance to the object is determined depending on thetime duration determined.